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Date: Sat, 24 Feb 2024 19:59:41 -0800
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Subject: Re: [syzbot] Re: [syzbot] [virtualization?] KMSAN: uninit-value in
 virtqueue_add (4)
From: syzbot <syzbot+d7521c1e3841ed075a42@syzkaller.appspotmail.com>
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Subject: Re: [syzbot] [virtualization?] KMSAN: uninit-value in virtqueue_add (4)
Author: penguin-kernel@i-love.sakura.ne.jp

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.7

syzbot is reporting a false-positive KMSAN warning upon coredump, for
dump_emit_page() path reaches memcpy_from_iter_mc() via iterate_bvec()
by setting "struct iov_iter"->copy_mc to true.

Make arch/x86/lib/copy_mc.c not to call arch/x86/lib/copy_mc_64.S
when KMSAN is enabled.

Reported-by: syzbot <syzbot+d7521c1e3841ed075a42@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=d7521c1e3841ed075a42
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 arch/x86/lib/copy_mc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c
index 6e8b7e600def..c6a0b8dbf58d 100644
--- a/arch/x86/lib/copy_mc.c
+++ b/arch/x86/lib/copy_mc.c
@@ -61,9 +61,9 @@ unsigned long copy_mc_enhanced_fast_string(void *dst, const void *src, unsigned
  */
 unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len)
 {
-	if (copy_mc_fragile_enabled)
+	if (!IS_ENABLED(CONFIG_KMSAN) && copy_mc_fragile_enabled)
 		return copy_mc_fragile(dst, src, len);
-	if (static_cpu_has(X86_FEATURE_ERMS))
+	if (!IS_ENABLED(CONFIG_KMSAN) && static_cpu_has(X86_FEATURE_ERMS))
 		return copy_mc_enhanced_fast_string(dst, src, len);
 	memcpy(dst, src, len);
 	return 0;
@@ -74,14 +74,14 @@ unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, un
 {
 	unsigned long ret;
 
-	if (copy_mc_fragile_enabled) {
+	if (!IS_ENABLED(CONFIG_KMSAN) && copy_mc_fragile_enabled) {
 		__uaccess_begin();
 		ret = copy_mc_fragile((__force void *)dst, src, len);
 		__uaccess_end();
 		return ret;
 	}
 
-	if (static_cpu_has(X86_FEATURE_ERMS)) {
+	if (!IS_ENABLED(CONFIG_KMSAN) && static_cpu_has(X86_FEATURE_ERMS)) {
 		__uaccess_begin();
 		ret = copy_mc_enhanced_fast_string((__force void *)dst, src, len);
 		__uaccess_end();
-- 
2.34.1